1. Field of the Invention
The invention relates to camptothecin and analogs thereof which show life prologation effects in various leukemia systems such as P-388 and L-1210; inhibition of animal tumors such as B-16 melanoma and are potent inhibitors of topoisomerase I and a method of synthesizing the same by means of a novel hydroxyl-containing tricyclic intermediate. The invention also relates to a method for inhibiting topoisomerase I and treating colorectal cancer.
2. Discussion of the Background
Camptothecin is a pentacyclic alkaloid initially isolated from the wood and bark of Camptotheca acuminata by Wall et al (M. E. Wall, M. C. Wani, C. E. Cook, K. H. Palmer, A. T. McPhail, and G. A. Sim, J. Am. Chem. Soc., 94, 388 (1966).
Camptothecin is highly biologically active and displays strong inhibitory activity toward the biosynthesis of nucleic acids. Additionally, camptothecin exhibits potent anti-tumor activity against experimentally transplanted carcinoma such as leukemia L-1210 in mice or Walker 256 tumor in rats.
Several methods for the synthesis of camptothecin and camptothecin analogs are known. These synthetic methods include (i) methods in which naturally occurring camptothecin is synthetically modified to produce a number of analogs and (ii) totally synthetic methods.
U.S. Pat. Nos. 4,604,463; 4,545,880; and 4,473,692 as well as European Patent Application 0074256 are examples of the former type of synthetic strategy. Additional examples of this strategy can be found in Japanese Patents 84/46,284; 84/51,287; and 82/116,015. These methods require naturally occurring camptothecin which is difficult to isolate and hence these methods are not suitable for the production of large quantities of camptothecin or analogs.
Examples of a variety of totally synthetic routes to camptothecin and camptothecin analogs can be found in the following references: Sci Sin. (Engl. Ed), 21(1), 87-98 (1978); Fitoterpapia, 45(3), 87-101 (1974); Yakugaku Zashi, 92(6), 743-6 (1972); J. Org. Chem., 40(14), 2140-1 (1975); Hua Hsueh Hsueh Pao, 39 (2), 171-8 (1981); J. Chem. Soc., Perkin Trans 1, (5), 1563-8 (1981); Heterocycles, 14 (7), 951-3 (1980); J. Amer. Chem. Soc., 94(10), 3631-2 (1972); J. Chem. Soc. D, (7), 404 (1970) and U.S. Pat. No. 4,031,098.
Wani et al, J. Med. Chem., 23, 554 (1980) discloses a synthesis of camptothecin and camptothecin analogs which involves the reaction of a tricyclic compound with a suitably substituted orthoaminoaldehyde to yield desoxycamptothecin as shown in Equation 1 below. ##STR1##
Desoxycamptothecin is then treated with oxygen to give camptothecin analogs. A major disadvantage of this procedure is the insolubility of desoxycamptothecin and its analogs, requiring large solvent volumes in the final step. A poor yield of the oxygenation product results under these conditions.
There exists a need, therefore, for a high-yield, efficient synthesis of camptothecin and camptothecin analogs which does not require prior isolation of naturally occurring camptothecin.
A need also exists for a method of synthesizing camptothecin and camptothecin analogs which does not suffer from insolubility problems of intermediate compounds and the resulting low yields.
A further need exists for new camptothecin analogs which can be synthesized in an efficient, high-yield manner and which show good biological activity.